/Engine/Source/Runtime/WebBrowser/Public/IWebBrowserCookieManager.h
Removes all matching cookies. Leave both URL and CookieName blank to delete the entire cookie database. The actual deletion will be scheduled on the browser IO thread, so the operation may not have completed when the function returns.
void DeleteCookies ( const [FString](API\Runtime\Core\Containers\FString) & URL, const [FString](API\Runtime\Core\Containers\FString) & CookieName, [TFunction](API\Runtime\Core\GenericPlatform\TFunction)< void(int)> Completed )